High-gain Cell-level all-GaN-based DC-DC Resonant Converter System for Grid-tied Energy Storage Systems

In Phase-I project, we propose to design, control, optimize, develop, and experimentally characterize a system of energy storage-integrated dc-dc power electronic converters that produce well-regulated 360V dc link from 2.5V-4V cell output DC at 2kW rated load. The proposed dc-dc system allows bidirectional power flow, thereby flexibly facilitating cell charging from solar photovoltaic or any other energy source ports as well. In state-of-the-art (SOA) grid-integrated energy storage systems, a large number of series-connected cells form a battery module, which is then fed to a single high-power-rated dc-dc converter to form a fixed DC link for the follow-on inverter stage. In such architectures, failure of a single cell might collapse the entire dc link, resulting in a compromise of the battery-to-grid end-to-end power flow and hence extremely poor structural modularity. To address these issues, the concept of cell-level Power Electronics (cPE) with integrated thermal management is explored to make the architecture more fault-tolerant, robust, smart, and scalable. Addressing the research gaps and technological needs, the specific research problems to be addressed in this project are: (a) development of efficient, compact power conversion topologies for the required ultra-high gain conversion (cell voltage to DC bus voltage), (b) synthesis and development of supervisory level optimal power split control of the cPE units for module-level efficiency maximization, (c) switching and conduction loss minimization in the corner operating conditions with cell voltage depletion and hence an even higher step-up gain requirement, (d) strategies for integration of magnetic components, and (e) thermal management optimization. Enhanced device properties of wide bandgap (WBG) semiconductors (Gallium Nitride, or GaN, in this work) will be leveraged to design a high-frequency efficient power conversion system with reduced passive component footprints. The proposed system is estimated to exhibit a power density of 5W/inch3 and dimensions of (2 in. x 5 in. x 2 in.) and to be 98% efficient at rated load and nominal state-of-charge (SoC) conditions. Specific focus areas of phase-I work include: (a) optimization of high-gain resonant dc-dc converter systems through multivariable modulation-based RMS current minimization and softswitching enhancements, (b) supervisory level optimal power split control of the modular converter system for efficiency maximization, (c) highly efficient active cell balancing mechanism with uniformized SoC, and (d) passive component optimization for power density enhancement through implementation of planar magnetics.